Circulating tumor DNA functions as an alternative for tissue to overcome tumor heterogeneity in advanced gastric cancer

Overcoming tumor heterogeneity is a major challenge for personalized treatment of gastric cancer, especially for human epidermal growth factor receptor‐2 targeted therapy. Analysis of circulating tumor DNA allows a more comprehensive analysis of tumor heterogeneity than traditional biopsies in lung cancer and breast cancer, but little is known in gastric cancer. We assessed mutation profiles of ctDNA and primary tumors from 30 patients with advanced gastric cancer, then performed a comprehensive analysis of tumor mutations by multiple biopsies from five patients, and finally analyzed the concordance of HER2 amplification in ctDNA and paired tumor tissues in 70 patients. By comparing with a single tumor sample, ctDNA displayed a low concordance of mutation profile, only approximately 50% (138/275) somatic mutations were found in paired tissue samples, however, when compared with multiple biopsies, most DNA mutations in ctDNA were also shown in paired tumor tissues. ctDNA had a high concordance (91.4%, Kappa index = 0.784, P < 0.001) of HER2 amplification with tumor tissues, suggesting it might be an alternative for tissue. It implied that ctDNA‐based assessment could partially overcome the tumor heterogeneity, and might serve as a potential surrogate for HER2 analysis in gastric cancer.     

Clonal dynamics of circulating tumor DNA during immune checkpoint blockade therapy for melanoma

Assessment of treatment efficacy of immune checkpoint inhibitors in melanoma patients is difficult as the response to these therapies varies among patients or lesions. The clonal evolution of cancer during immune checkpoint blockade therapy could cause treatment resistance. We investigated the potential of liquid biopsy in monitoring the mutational profiles of metastatic melanoma during immunotherapy. Plasma samples collected from 21 Japanese metastatic melanoma patients before immune checkpoint blockade therapy were subjected to whole-exome sequencing (WES). Furthermore, 14 Japanese patients with melanoma were enrolled for longitudinal analysis of circulating tumor DNA (ctDNA). Plasma samples were collected prospectively before and during therapy and sequenced. WES of the pretreatment plasma from Japanese melanoma patients showed detectable ctDNA levels with wide ranges of variant allele frequencies within a sample, suggesting clonal and subclonal mutations in ctDNA. In targeted sequencing using longitudinal samples, ctDNA levels correlated with increased tumor size, while ctDNA content immediately decreased after a surge in a patient exhibiting pseudo-progression, suggesting the potential of ctDNA analysis in discriminating between pseudo- and true progression. Mutant ctDNA levels showed different patterns within the clinical course of specific patients, suggesting that these mutations were derived from different tumor clones with distinct therapeutic responses. During further investigation, WES of plasma samples from 1 patient showed marked differences in the mutational profiles of ctDNA, including expansive tumor evolution during an acute exacerbation. Immunotherapy may induce characteristic clonal evolutions of tumors; longitudinal analysis of ctDNA has the potential of determining these tumor evolution patterns and therapeutic responses.     

Serial circulating tumor DNA to predict early recurrence in patients with hepatocellular carcinoma: a prospective study

We studied the value of circulating tumor DNA (ctDNA) in predicting early postoperative tumor recurrence and monitoring tumor burden in patients with hepatocellular carcinoma (HCC). Plasma‐free DNA, germline DNA, and tissue DNA were isolated from 41 patients with HCC. Serial ctDNAs were analyzed by next‐generation sequencing before and after operation. Whole‐exome sequencing was used to detect the DNA of HCC and adjacent tissues. In total, 47 gene mutations were identified in the ctDNA of the 41 patients analyzed before surgery. ctDNA was detected in 63.4% and 46% of the patient plasma pre‐ and postoperation, respectively. The preoperative ctDNA positivity rate was significantly lower in the nonrecurrence group than in the recurrence group. With a median follow‐up of 17.7 months, nine patients (22%) experienced tumor recurrence. ctDNA positivity at two time‐points was associated with significantly shorter recurrence‐free survival (RFS). Tumors with NRAS, NEF2L2, and MET mutations had significantly shorter times to recurrence than those without mutations and showed high recurrence prediction performance by machine learning. Multivariate analyses showed that the median variant allele frequency (VAF) of mutations in preoperative ctDNA was a strong independent predictor of RFS. ctDNA is a real‐time monitoring indicator that can accurately reflect tumor burden. The median VAF of baseline ctDNA is a strong independent predictor of RFS in individuals with HCC.     

Circulating tumor DNA as a non‐invasive substitute to metastasis biopsy for tumor genotyping and personalized medicine in a prospective trial across all tumor types

Cell‐free tumor DNA (ctDNA) has the potential to enable non‐invasive diagnostic tests for personalized medicine in providing similar molecular information as that derived from invasive tumor biopsies. The histology‐independent phase II SHIVA trial matches patients with targeted therapeutics based on previous screening of multiple somatic mutations using metastatic biopsies. To evaluate the utility of ctDNA in this trial, as an ancillary study we performed de novo detection of somatic mutations using plasma DNA compared to metastasis biopsies in 34 patients covering 18 different tumor types, scanning 46 genes and more than 6800 COSMIC mutations with a multiplexed next‐generation sequencing panel. In 27 patients, 28 of 29 mutations identified in metastasis biopsies (97%) were detected in matched ctDNA. Among these 27 patients, one additional mutation was found in ctDNA only. In the seven other patients, mutation detection from metastasis biopsy failed due to inadequate biopsy material, but was successful in all plasma DNA samples providing three more potential actionable mutations. These results suggest that ctDNA analysis is a potential alternative and/or replacement to analyses using costly, harmful and lengthy tissue biopsies of metastasis, irrespective of cancer type and metastatic site, for multiplexed mutation detection in selecting personalized therapies based on the patient''s tumor genetic content.     

Targeted Next-Generation Sequencing of Circulating Tumor DNA Mutations among Metastatic Breast Cancer Patients

Liquid biopsy through the detection of circulating tumor DNA (ctDNA) has potential advantages in cancer monitoring and prediction. However, most previous studies in this area were performed with a few hotspot genes, single time point detection, or insufficient sequencing depth. In this study, we performed targeted next-generation sequencing (NGS) with a customized panel in metastatic breast cancer (MBC) patients. Fifty-four plasma samples were taken before chemotherapy and after the third course of treatment for detection and analysis. Paired lymphocytes were also included to eliminate clonal hematopoiesis (CH)-related alternatives. A total of 1182 nonsynonymous mutations in 419 genes were identified. More ctDNA mutations were detected in patients with tumors > 3 cm (p = 0.035) and HER2(−) patients (p = 0.029). For a single gene, the distribution of ctDNA mutations was also correlated with clinical characteristics. Multivariate regression analysis revealed that HER2 status was significantly associated with mutation burden (OR 0.02, 95% CI 0–0.62, p = 0.025). The profiles of ctDNA mutations exhibited marked discrepancies between two time points, and baseline ctDNA was more sensitive and specific than that after chemotherapy. Finally, elevated ctDNA mutation level was positively correlated with poor survival (p < 0.001). Mutations in ctDNA could serve as a potential biomarker for the evaluation, prediction, and clinical management guidance of MBC patients with chemotherapy.     

Analysis of ctDNA to predict prognosis and monitor treatment responses in metastatic pancreatic cancer patients

Cell‐free circulating tumor DNA (ctDNA) in plasma has been used as a potential noninvasive biomarker for various tumors. Our study was performed to evaluate the clinical implications of ctDNA detection in patients with metastatic pancreatic cancer. First, we attempted to prospectively screen a panel of 60 genes in cell‐free DNA (cfDNA) from ten metastatic pancreatic cancer patients via exome sequencing. Second, droplet digital PCR (ddPCR) was used to identify potential mutations in a cohort of 188 patients with metastatic pancreatic cancer. Finally, to preliminary evaluate the potential role of ctDNA in monitoring tumor responses following chemotherapy, we detected the presence of ctDNA in serial plasma samples from 13 metastatic pancreatic cancer patients (Clinical trial: NCT02017015). The analysis revealed five somatic mutations at BRCA2, EGFR, KDR and ERBB2 gene loci. The frequencies of ctDNA mutation at BRCA2, KDR, EGFR, ERBB2 exon17 and ERBB2 exon27 were 11.7%, 13.8%, 13.3%, 13.3% and 6.4% respectively. Univariate and multivariate analyses identified the ERBB2 exon17 mutation (p = 0.035, HR = 1.61) as an independent factor associated with overall survival among metastatic pancreatic cancer patients. Furthermore, the rate of coincident detection of ctDNA and response to treatment as assessed by CT imaging was 76.9% (10 of 13 cases), and the presence of ctDNA provided the earliest measure of treatment in 6 of 10 patients (60%). ctDNA sequencing may have clinical value for determining metastatic pancreatic cancer treatment and monitoring the tumor response.     

Circulating tumor DNA and circulating tumor cells in metastatic triple negative breast cancer patients

Circulating tumor DNA (ctDNA) is a new circulating tumor biomarker which might be used as a prognostic biomarker in a way similar to circulating tumor cells (CTCs). Here, we used the high prevalence of TP53 mutations in triple negative breast cancer (TNBC) to compare ctDNA and CTC detection rates and prognostic value in metastatic TNBC patients. Forty patients were enrolled before starting a new line of treatment. TP53 mutations were characterized in archived tumor tissues and in plasma DNA using two next generation sequencing (NGS) platforms in parallel. Archived tumor tissue was sequenced successfully for 31/40 patients. TP53 mutations were found in 26/31 (84%) of tumor samples. The same mutation was detected in the matched plasma of 21/26 (81%) patients with an additional mutation found only in the plasma for one patient. Mutated allele fractions ranged from 2 to 70% (median 5%). The observed correlation between the two NGS approaches (R² = 0.903) suggested that ctDNA levels data were quantitative. Among the 27 patients with TP53 mutations, CTC count was ≥1 in 19 patients (70%) and ≥5 in 14 patients (52%). ctDNA levels had no prognostic impact on time to progression (TTP) or overall survival (OS), whereas CTC numbers were correlated with OS (p = 0.04) and marginally with TTP (p = 0.06). Performance status and elevated LDH also had significant prognostic impact. Here, absence of prognostic impact of baseline ctDNA level suggests that mechanisms of ctDNA release in metastatic TNBC may involve, beyond tumor burden, biological features that do not dramatically affect patient outcome.     

循环肿瘤DNA在脑胶质瘤中的研究进展

脑胶质瘤是脑内最常见的原发性恶性肿瘤,包括多种亚型,预后各异。其病变部位特殊,手术切除较困难,后续治疗方法极为有限。在精准医疗时代,发现肿瘤驱动基因或驱动突变、鉴定其特殊DNA突变模式已成为现代肿瘤学研究的重点和难点。常规肿瘤组织活检仅提供了单一部位、单一时间的肿瘤细胞信息,不能充分描述肿瘤基因组异质性及其动态变化的全景特征。循环肿瘤DNA（circulating tumor DNA,ctDNA）监测以非侵入性的方式连续观察肿瘤基因组的变化,为癌症诊断、治疗反应和预后判断提供有价值的生物标志物。本文回顾ctDNA在脑胶质瘤中的研究进展,对其检测方法及在早期诊断、反映肿瘤突变负荷、监测疗效和反映肿瘤细胞的异质性等方面的研究进行系统综述。      

Assessing tumor heterogeneity using ctDNA to predict and monitor therapeutic response in metastatic breast cancer

Tumor heterogeneity was associated with treatment outcome of metastatic cancers but few studies have examined whether tumor heterogeneity in circulating tumor DNA (ctDNA) can be used to predict treatment outcome. ctDNA analysis was performed in 37 HER2-positive metastatic breast cancer patients treated with pyrotinib. Patients with high tumor heterogeneity had significantly worse PFS outcomes, with a median PFS of 30.0 weeks vs. 60.0 weeks for patients with low tumor heterogeneity (hazard ratio [HR], 2.9; p = 0.02). Patients with trunk resistance mutations receiving pyrotinib monotherapy had worse outcomes (HR, 4.5; p = 0.03), with a median PFS of 7.8 weeks vs. 27.4 weeks for those with branch resistance mutations or without any resistance mutations in baseline ctDNA. Longitudinal monitoring of 21 patients during treatment showed that the molecular tumor burden index ([mTBI] a measure of the percentage of ctDNA in samples) was positively correlated with tumor size as evaluated by computed tomography (p < 0.0001, Pearson r = 0.52) and detected disease progression 8–16 weeks earlier. Our current findings suggested that ctDNA could be used to assess tumor heterogeneity and predict treatment outcomes. Furthermore, the mTBI is better for assessing therapeutic response than single gene mutations and might supplement the current therapeutic response evaluation system.     

Post-radiation circulating tumor DNA as a prognostic factor in locally advanced esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a highly malignant and deadly tumor. Radiation therapy is one of the primary treatments for locally advanced ESCC. However, the biomarkers for prognosis of definitive radiation remain undefined. Peripheral blood circulating tumor (ct)DNA provides information of tumor genetic alterations and has been confirmed as a potential non-invasive biomarker for several types of cancer. The present study investigated the clinical implications of ctDNA detection in patients with ESCC and receiving definitive radiation therapy. Patients with locally advanced ESCC were retrospectively recruited. Plasma samples were collected before, during and following radiation therapy. Next-generation sequencing was performed to identify somatic mutations in 180 genes. A total of 69 baseline and post-radiation plasma samples were collected from 25 patients. A total of 59 non-silent single nucleotide variants were present in 33 genes. All pre-radiation and 58.3% (14/24) of post-radiation samples had at least one mutation. Patients with lymph node metastases (LNM) exhibited a higher number of pre-radiation mutations compared with those without LNM. The variables, progression-free survival (PFS) and overall survival (OS) of the patients with one baseline mutation were not significantly different compared with that in patients with more than one baseline mutation. Patients with initial ctDNA-positive post-radiation samples exhibited significantly reduced PFS (P=0.047) and OS (P=0.005) compared with that in patients with ctDNA-negative samples. The post-radiation plasma ctDNA status was an independent prognostic factor from univariate and multivariate analyses. Dynamic monitoring of ctDNA during follow-up was examined. The results indicated that ctDNA was a predictive and prognostic marker in patients with ESCC and receiving definitive radiation therapy, which may guide subsequent treatment.     

Cell-free circulating tumor DNA in cancer

Cancer is a common cause of death worldwide. Despite significant advances in cancer treatments, the morbidity and mortality are still enormous. Tumor heterogeneity, especially intratumoral heterogeneity, is a significant reason under-lying difculties in tumor treatment and failure of a number of current therapeutic modalities, even of molecularly targeted therapies. The development of a virtually noninvasive“liquid biopsy”from the blood has been attempted to characterize tumor heterogeneity. This review focuses on cell-free circulating tumor DNA (ctDNA) in the bloodstream as a versatile biomarker. ctDNA analysis is an evolving field with many new methods being developed and optimized to be able to successfully extract and analyze ctDNA, which has vast clinical applications. ctDNA has the potential to accurately genotype the tumor and identify personalized genetic and epigenetic alterations of the entire tumor. In addition, ctDNA has the potential to accurately monitor tumor burden and treatment response, while also being able to monitor minimal residual disease, reducing the need for harmful adjuvant chemotherapy and allowing more rapid detection of relapse. There are still many challenges that need to be overcome prior to this biomarker getting wide adoption in the clinical world, including optimization, standardization, and large multicenter trials.     

Genomic alterations in plasma DNA from patients with metastasized prostate cancer receiving abiraterone or enzalutamide

In patients with metastatic castrate‐resistant prostate cancer (mCRPC), circulating tumor DNA (ctDNA) analysis offers novel opportunities for the development of non‐invasive biomarkers informative of treatment response with novel agents targeting the androgen‐receptor (AR) pathway, such as abiraterone or enzalutamide. However, the relationship between ctDNA abundance, detectable somatic genomic alterations and clinical progression of mCRPC remains unexplored. Our study aimed to investigate changes in plasma DNA during disease progression and their associations with clinical variables in mCRPC patients. We analyzed ctDNA in two cohorts including 94 plasma samples from 25 treatment courses (23 patients) and 334 plasma samples from 125 patients, respectively. We conducted whole‐genome sequencing (plasma‐Seq) for genome‐wide profiling of somatic copy number alterations and targeted sequencing of 31 prostate cancer‐associated genes. The combination of plasma‐Seq with targeted AR analyses identified prostate cancer‐related genomic alterations in 16 of 25 (64%) treatment courses in the first cohort, in which we demonstrated that AR amplification does not always correlate with poor abiraterone and enzalutamide therapy outcome. As we observed a wide variability of ctDNA levels, we evaluated ctDNA levels and their association with clinical parameters and included the second, larger cohort for these analyses. Employing altogether 428 longitudinal plasma samples from 148 patients, we identified the presence of bone metastases, increased lactate dehydrogenase and prostate‐specific antigen (PSA) as having the strongest association with high ctDNA levels. In summary, ctDNA alterations are observable in the majority of patients with mCRPC and may eventually be useful to guide clinical decision‐making in this setting.     

Capturing intra-tumor genetic heterogeneity by de novo mutation profiling of circulating cell-free tumor DNA: a proof-of-principle

BackgroundPlasma-derived cell-free tumor DNA (ctDNA) constitutes a potential surrogate for tumor DNA obtained from tissue biopsies. We posit that massively parallel sequencing (MPS) analysis of ctDNA may help define the repertoire of mutations in breast cancer and monitor tumor somatic alterations during the course of targeted therapy.Patient and methodsA 66-year-old patient presented with synchronous estrogen receptor-positive/HER2-negative, highly proliferative, grade 2, mixed invasive ductal–lobular carcinoma with bone and liver metastases at diagnosis. DNA extracted from archival tumor material, plasma and peripheral blood leukocytes was subjected to targeted MPS using a platform comprising 300 cancer genes known to harbor actionable mutations. Multiple plasma samples were collected during the fourth line of treatment with an AKT inhibitor.ResultsAverage read depths of 287x were obtained from the archival primary tumor, 139x from the liver metastasis and between 200x and 900x from ctDNA samples. Sixteen somatic non-synonymous mutations were detected in the liver metastasis, of which 9 (CDKN2A, AKT1, TP53, JAK3, TSC1, NF1, CDH1, MML3 and CTNNB1) were also detected in >5% of the alleles found in the primary tumor sample. Not all mutations identified in the metastasis were reliably identified in the primary tumor (e.g. FLT4). Analysis of ctDNA, nevertheless, captured all mutations present in the primary tumor and/or liver metastasis. In the longitudinal monitoring of the patient, the mutant allele fractions identified in ctDNA samples varied over time and mirrored the pharmacodynamic response to the targeted therapy as assessed by positron emission tomography–computed tomography.ConclusionsThis proof-of-principle study is one of the first to demonstrate that high-depth targeted MPS of plasma-derived ctDNA constitutes a potential tool for de novo mutation identification and monitoring of somatic genetic alterations during the course of targeted therapy, and may be employed to overcome the challenges posed by intra-tumor genetic heterogeneity.Registered clinical trialwww.clinicaltrials.gov, NCT01090960.     

非小细胞肺癌患者组织与血清ctDNA突变频谱的一致性及其相关因素分析

目的:探究非小细胞肺癌（NSCLC）患者组织与血清循环肿瘤DNA（ctDNA）突变频谱的一致性及其相关因素分析。方法:选取2019年01月至2019年06月在河北大学附属医院诊断及治疗的NSCLC患者50例，检测所有患者肿瘤组织及ctDNA基因突变情况，同时搜集患者肿瘤相关临床资料，根据基因一致性情况将患者分为一致组与不一致组，使用Logistic回归分析影响一致性的相关因素。结果:肿瘤组织中至少存在一种突变的为96%（48/50），血清中至少存在一种突变的为64%（32/50），组织学与血清ctDNA检测结果一致率为46%（23/50）;一致组年龄显著小于不一致组，组织学分级中低分化人数比例、Ⅳ期人数比例、肿瘤＞3 cm人数比例、骨转移人数比例显著高于不一致组（P＜0.05），多因素Logistic回归分析显示，组织低分化（OR=2.802，P=0.028）、Ⅳ期（OR=8.922，P=0.004）、有骨转移（OR=8.425，P=0.012）是基因突变检测一致性的独立危险因素。结论:NSCLC患者组织与血清ctDNA突变频率一致性受多种因素影响，分化越低，分期越高、伴骨转移的一致性越高。     

Multi‐regional sequencing reveals intratumor heterogeneity and positive selection of somatic mtDNA mutations in hepatocellular carcinoma and colorectal cancer

Recent studies have revealed significant intratumor heterogeneity (ITH) of nuclear genome mutations and highlighted its function in tumor progression and treatment resistance. However, the ITH of somatic mitochondrial DNA (mtDNA) mutations detected in cancers remains unknown. In this study, we performed multiregional mtDNA sequencing of tumor and paratumor tissue samples from 12 hepatocellular carcinoma (HCC) and 13 colorectal cancer (CRC) patients. A substantial level of mtDNA mutations was found in paired non‐HCC inflammatory tissues, suggesting that these tissues might not be mtDNA‐genetically “normal.” Moreover, our data indicated that the ITH of somatic mtDNA mutations was a common feature in HCC and CRC patients. In addition, we found that shared mutations which were observed in at least 2 samples in each patient exhibited a significantly higher heteroplasmic level than mutations that were private to a specific tumor region from both HCC (p = 0.039) and CRC patients (p = 0.001). The heteroplasmic level of shared mutations was positively correlated with intratumoral recurrence of mtDNA mutations. We also found that shared mutations in tumor tissues with a higher degree of pathogenicity risk exhibited a higher heteroplasmic level and intratumoral recurrence in both HCC and CRC patients. These findings suggest that some mtDNA mutations may undergo positive selection during the clonal expansion. Taken together, our analyses identified various levels of ITH of somatic mtDNA mutations in HCC and CRC patients and provided evidence supporting the positive selection working on some somatic mtDNA mutations in tumor tissues.     

Plasma clearance of RAS mutation under therapeutic pressure is a rare event in metastatic colorectal cancer

In metastatic colorectal cancer (mCRC), circulating tumor DNA (ctDNA) monitoring can be used to genotype tumors and track clonal evolution. We investigated the clearance of RAS mutated clones under chemotherapy pressure by ctDNA analysis in patients with a RAS mutated mCRC. Patients with a RAS mutated tumor included in the prospective PLACOL study were monitored for ctDNA. Analyses were based on optimized targeted next-generation sequencing and/or droplet-based digital polymerase chain reaction (ddPCR). For plasma samples without detectable mutations at progression disease, we tested the methylation status of WIF1 and NPY genes using methylation-ddPCR (met-ddPCR) to validate the presence of ctDNA. Among the 36 patients with positive plasma samples for RAS mutations at inclusion, 28 (77.8%) remained RAS positive at disease progression and 8 (22.2%) became negative. Subsequent met-ddPCR for methylated markers showed that only two out of the eight patients with RAS negative plasma had detectable ctDNA at progression. Therefore, only 2 samples among 36 were confirmed for clearance of RAS mutation in our series. In conclusion, this study suggests that the clearance of RAS mutations in patients treated by chemotherapy for a RAS mutated mCRC is a rare event. Monitoring tumor mutations in plasma samples should be combined with a strict control of the presence of ctDNA. The therapeutic impacts of RAS clearance need to be further explored.     

The feasibility of using mutation detection in ctDNA to assess tumor dynamics

For many decades it has been known that tumor DNA is shed into the blood. As a consequence of technological limitations, researchers were unable to comprehensively characterize circulating DNA. The advent of ultrasensitive and highly specific molecular assays has provided a comprehensive profile of the molecular characteristics and dynamics of circulating DNA in healthy subjects and cancer patients. With these new tools in hand, significant interest has been provoked for an innovative type of tumor biopsy termed a “liquid biopsy”. Liquid biopsies are obtained by minimal invasive blood draws from cancer patients. Circulating cancer cells, exosomes and a variety of molecules contained within the liquid biopsy including cell‐free circulating tumor DNA (ctDNA) can serve as promising tools to track cancer evolution. Attractive features of ctDNA are that ctDNA isolation is straightforward, ctDNA levels increase or decrease in response to the degree of tumor burden and ctDNA contains DNA mutations found in both primary and metastatic lesions. Consequently, the analysis of circulating DNA for cancer‐specific mutations might prove to be a valuable tool for cancer detection. Moreover, the capacity to screen for ctDNA in serial liquid biopsies offers the possibility to monitor tumor progression and responses to therapy and to influence treatment decisions that ultimately may improve patient survival. Here we focus on mutation detection in ctDNA and provide an overview of the characteristics of ctDNA, detection methods for ctDNA and the feasibility of ctDNA to monitor tumor dynamics. Current challenges associate with ctDNA will also be discussed.     

晚期胃癌患者血液ctDNA水平与组织学基因检测的一致性比较

目的:比较晚期胃癌患者外周血循环肿瘤DNA（circulating tumor DNA,ctDNA）与组织学基因检测的一致性,讨论ctDNA的临床应用价值。方法:根据纳排标准最终收集30例晚期初诊初治胃癌患者的实体组织标本及血浆标本,并用二代测序(next generationg sequencing,NGS)技术分别检测68个基因在其中的表达状况。对比ctDNA与组织学检测基因的检出一致性及差异,评估其用于诊断胃癌的敏感度、特异度。并按胃癌突变基因分层进一步评估ctDNA的检出率。结果:30例患者中检出的基因突变总共138个,其中组织学标本中总共检出71个,ctDNA中总共检出67个。ctDNA对比组织学检测基因诊断胃癌的灵敏度为31.5%,特异度为63.6%,一致率为43.3%。单基因检测分析突变最多的基因前三位为TP53、PIK3CA、HER-2。其中对PIK3CA的检测,组织学和ctDNA两种方法差异有统计学意义（P＜0.05）。TP53、PIK3CA、HER-2、EGFR、KRAS在组织学中检出丰度大于1,但在ctDNA中小于1。有PIK3CA突变的患者中,共存的其他致癌基因突变位点包括KRAS 2例、BRAF 2例、EGFR 4例。有HER-2突变的患者中,共存PIK3CA突变者4例,共存KRAS突变者3例。结论:ctDNA检测虽然在晚期胃癌患者的诊断中敏感度、特异度低于组织标本基因检测,但其标本易获、接受度高,可作为基因检测的补充、备选。实体组织检出相同基因的突变丰度总体高于ctDNA。TP53、PIK3CA、HER-2、EGFR等基因在ctDNA中的检出有利于指导胃癌治疗及预后评估,尤其PIK3CA在ctDNA中高于组织中的检出率。ctDNA检测可为胃癌患者的精准靶向治疗提供依据。